1. Field of the Invention
The present invention relates to a process for manufacturing a universal joint by cold forging, and more particularly to a process for forming from sheet metal a cylindrical hub to be connected to a rotary driving shaft and a pair of forks facing each other to be connected to a cross-arm.
2. Description of the Prior Art
It has been known in the prior art to manufacture a universal joint from a sheet metal blank by subjecting the same to several processing steps. For example, as shown in FIG. 1 the universal joint has heretofore been formed from a blank 1 which is made as an element of such a universal joint as shown in FIG. 2 by punching it out of the sheet metal and is comprised of a hub member portion 2 to form a cylindrical hub, a pair of bending edge member portions 3 to form lug portions abutted to both edges of the hub member portion 2 and protruding from the cylinder to be bolted to retain the hub in a cylindrical shape, and a pair of fork member portions 4 to form forks extending at right angles from the hub member portion 2 and connecting to both ends of one shaft of the cross arm elements 5 for the universal joint. Then, the hub portion is bent to a cylindrical shape and its inner circumferential surface is spline-milled to make it possible to connect to the rotary driving shaft formed onto the spline shaft. Also, the lug portions to be bolted are bent in order to bore the bolt holes and secure the bolting.
However such a conventional process inevitably further requires two additional steps; one is to bend the bending edge member portions and another is to cut the thus bent-up portions so as not to hinder the spline milling. Furthermore, since the bending edge member portions 3 must be added to both edges of the hub member portion 2, the length of blank 1 naturally becomes long and in consequence, taking an area of fork member portions 4 into consideration, a rate of material utilization in the blanking step becomes considerably low. Thus in the prior art there were some drawbacks such that several extra processes are required and a waste of time and material are brought about.